Microdroplet Magnetic Field Sensor Utilizing Magneto‐Birefringence Effect

Abstract Despite advancements in magnetometry, achieving precise, real‐time local magnetic field sensing in microscale systems remains a significant challenge. Here, a compact and versatile magnetic field sensor is presented that utilizes magnetically induced birefringence in micrometer‐sized droplets of an isotropic suspension of magnetic nanoplatelets. By measuring the light intensity with crossed polarizers, it is demonstrated that the sensor's capability to detect magnetic fields in the millitesla range with high sensitivity. Experimental results, supported by numerical simulations, confirm the sensor's accuracy and robustness. Its practical application is validated by measuring the magnetic field of a bent current‐carrying wire at the microscale. Additionally, a method is introduced for determining both the magnitude and direction of an unknown field using a specialized polarization camera. This novel approach offers a promising pathway for precise, real‐time magnetic field sensing in microfluidic and lab‐on‐chip applications, combining high spatial resolution with optical detection advantages.